Fixed #37. Don't allow banned users from logging in.

We use the user json returned from backend to decide whether user should log in or not. If user is banned, we don't allow user to enter. Send them back to login page with a brief line stating they are banned.
Fixed #39. Name and description fields are required now for add-group from.
Merge pull request #40 from yeukhon/issue39

Fixed 39. Require name and description fields.